This invention relates to a water treatment method and an apparatus, and more particularly, to a method and apparatus for the removal from aqueous fluid of toxic and potentially hazardous organic compounds. The present method and apparatus exploit, synergistically, ultraviolet photolysis, the use of hydroxyl radicals, and microwave energy to, optimize the oxidation of organic contaminants in water.
The use of ultraviolet light and oxidants, such as ozone and hydrogen peroxide, to produce hydroxyl radicals, is well-known. Such a technique has been used to enhance oxidation of organic contaminants in industrial waste water, groundwater and other aqueous solutions. Direct photolysis of organic compounds by intense ultraviolet light is also well known and is used extensively in the water treatment industry. Microwave radiation (electromagnetic waves having a wavelength between about 0.3 and 30 centimeters) is commonly used to induce rapid heating of materials from within by oscillatory stimulation of hydrogen and nitrogen atoms within water and organic molecules. Oxidation of organic contaminants by ultraviolet light or by chemical reaction with hydrogen peroxide ultimately yields innocuous products: carbon dioxide, elemental carbon, water and oxygen.
It has now been found that exploitation of the above techniques in a single compact apparatus creates a potent oxidative water treatment method.
Existing apparatus and methods, using ultraviolet (UV) light and reagents such as hydrogen peroxide to create hydroxyl radicals, are able to treat substantial volumes of water, on the order of hundreds of gallons per minute. In "first generation" systems of this sort, it was proposed that low pressure UV discharge lamps be encased in quartz tubes immersed in tanks of water to be treated. Hydrogen peroxide was added to the water, and the mixture was allowed to flow around the submerged lamps. Problems with rapid fouling of the lamps and low production of hydroxyl radicals in such devices soon became apparent. Second generation apparatus of the above type incorporated manual cleaning mechanisms, and the use of polymer coatings (such as "Teflon" PTFE) on the quartz sleeve, additional oxidizers (such as ozone), and catalyzing additives (such as TiO.sub.2) to enhance the rate of radical production. Lasers also have been used in efforts to increase energy transfer efficiency. Some efforts were successful to some extent, but at the price of significantly greater complexity and cost.
In known prior art apparatus and methods, the oxidizing reagent is added to the water prior to exposure of the mixture to the UV radiation. Since chemical oxidation is rapid, in such arrangements inorganic precipitates quickly form on the quartz sleeve or window surfaces, resulting in immediate and cumulative attenuation of the UV radiation.
Moreover, in known prior art apparatus and methods, addition of the oxidizing reagent to the water prior to UV exposure results in dilution of the reagent, so that the photon density of the UV radiation reaching the oxidant molecules is reduced by preferential absorption by the water, scattering and absorption by entrained particles in the water, and absorption by solutes. Sluggish mixing of the solution during irradiation also minimizes contact of the few radicals that are produced close to the light source, resulting in a relatively inefficient and certainly less than optimal capability for contaminant destruction.
The present invention provides a method and apparatus which addresses and obviates the above shortcomings of the prior art, by synergistically enhancing contaminant destruction by complementary techniques.